Need Help with Motor Driver

Hi, I have been using the SmartDriveDuo Smart Dual Channel 30A Motor Driver on a power wheelchair base that has 2 x 320W 24V DC brushed motors. It seems to work well, however I have been modifying the robot so I can use it as a snowplow. Now, with the added loads and stress to the motors, I find that they don’t respond to my controls as well - they tend to stutter, rather than accelerate smoothly. Is this because the motor controller can’t properly handle the power or is it another issue? Any information and/or clarification would be great!

Thank you,

Hi, I posted an inquiry here regarding cogging while using the SmartDriveDuo and the inquiry was moved to another location where it has not received any feedback. I posted it here as this thread mentions that the SmartDriveDuo is designed to drive medium powered motors - what exactly classifies medium powered? I have it running 2 x 320W 24vdc motors, however when load is applied, cogging occurs (I called it ‘stuttering’ in the post as I was not aware of the term). Are you able to provide and comments? Thank you!

Hello @Alexcp3o,

Yes, it was transferred to a different topic because this topic was only about suggestions while what you need is technical support. Either way, when you are using a motor driver you have to keep the following things in mind:

  • Nominal voltage: The SmartDriveDuo supports motor voltages from 7V to 35V so this should work for your 24vdc motors.
  • Continuous current: The SmartDriveDuo can provide 30A continuously to each channel. I’m not sure if you have all the specs of the motors you are using but I’m going to assume that the motors draw around 15A continuosly.
  • Maximum current: The SmartDriveDuo can provide 80A peak for only 1 second but luckily it has thermal/current limit protection.

As you mention the problems occur when you try to accelerate, I’m guessing that in this case the motors stall and the motor driver can’t provide enough current which may trigger the limit protections making your motors “stutter”. So most likely the problem is that the controller is not powerful enough for your motors.

Thanks for your reply, @geraldinebc15!

Would there be a risk if I added another 12v battery in series to increase the voltage do add that extra power?

As for the specs for the motors, this is what I found:

It seems to state 3.0A(max) - however this could mean something else.

Thanks again for your help, it is appreciated - I am very new to this and trying to understand as I go.

If you are already using 24V adding an extra battery won’t help because the power should be limited to what the motors need (24V) and what the motor driver can handle .

However, the specs you shared seem strange. The current stated there is quite low so it shouldn’t be causing the issues I mentioned earlier. So maybe the problem is that the motors aren’t powerful enough for your snowplow?

Try using this tool to check if everything seems right:


I used the sizing tool with the specs I have for the motors (form the wheelchair) and it comes out to what is expected, at around 350W and ~14amps - however on all similar motors I see online, they all say 3A max (How would that work, isn’t amperage correlated to V and w???). I don’t believe it’s an issue with the motors not being strong enough as the chair is designed to carry 225kg, additionally, I can position it up against a wall and accelerate and sometimes the wheels will just spin on spot rather than stutter. With all that being said, the SmartDriveDuo should be able to accommodate the motors (as per power, etc), however I read that it could be that because it is not sensored, it just basically pushes current on its own timing pattern to the motor. Would the Sabertooth be able to accommodate this better? Or am out to lunch and completely missing something?

Hello @Alexcp3o and @geraldinebc15,
you are both right, the specs on the motor are misleading. (3A idle current is my guess)
14-15A nominal current could easily mean 5-10 times higher stall current.
Spinning wheels when driving against a wall only indicates that the tire friction is lower than driving into a pile of snow.
My next best bet is weak(er) batteries from cold weather and the cogging is an undervoltage event.
What type of batteries are you using? LeadAcid are known to be bad below 4° Celsius.
Maybe adding a heater pad or using 2 more batteries in parallel will help.

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Thanks @o_lampe for your reply!

Currently I have 2 x 12V 80Ah deep cycle lead acid batteries (in series), however the unit is stored in a heated garage. The cogging did occur at times during the summer when I first put it together, but only when I was turning a certain direction. Now it seems to happen more often when I go straight forward or backward. I’ve tested the voltage on the batteries and they both hover around 11.5. Would that be enough undervoltage to cause cogging? If so, would adding a 3rd 6V be an option to provide the extra voltage?

Any thoughts on changing the motor controller to the Sabertooth - that one seems to be first choice among RC wheelchair conversion (based off of testimonies, videos, etc).

Thank you

Thanks @Alexcp3o for the details
Adding a 3rd battery only makes things worse:

  1. the motors would draw even more current => possible overcurrent event
  2. the undervoltage detection (should) check the voltage drop between idle and driving.
    That drop would increase, if we have a case of weak batteries.

Motors cogging during (hard) acceleration only or does it happen any time?
Maybe your motor-brushes are at end_of_life? Used brushed DC motors often need some service.
What about wiring-gauge? Thin wires or bad crimping can cause all sorts of errors.

I’d rule out all possible causes before thinking about another controller.

The cogging only happens when I first apply power / control to it from a stop. When this happens, I ease off the control and then re-apply a much more gently application to the joystick to allow a smooth acceleration. Once the motor turns smoothly, it can be accelerated faster without issue, it is only when it begins - either the cogging occurs and it doesn’t move (just stutters on the spot), or it starts no problem - it never happens during motion.

I will look into servicing the motors. And as for the wiring, I believe it should be good as I am using the existing wiring harness that came with the power chair, however I will look into the connections.

Something that I just thought of is that I had to upgrade the wheels to allow for more traction in the cold/snow. The new wheels came off of a snow blower and have a bigger radius (~50% increase). I would think that this would require additional torque to move them, which would need more power - could this be a reason why the cogging occurs? I know that the same motors are used on other devices that have larger wheels, so I don’t think it is too much for the motors to handle.

Finally, I used a multimeter to test the voltage on the batteries - unsure how I would test them while in motion and during acceleration.

Pics for reference on the wheels.

I recently built out a rc mower using the cytron 30x2 smart drive duo and getting the same cogging/stuttering issue. Swapped it out with a sabertooth 32x2 controller and the issue went away. I was testing both controllers when it was about 30 degrees F. I think I’ll eat the $50 premium and stick with sabertooth.

Thanks! I actually flipped mine while ripping around without the plow and damaged the controller, so I need to get a new one anyway. I’ll definitely get the sabertooth instead. I’ll also build a roll cage to protect it!